Structural and Functional CNS Abnormalities in Myotonic Dystrophy type 1 Myotonic dystrophy (DM), the most common form of muscular dystrophy, causes dramatic unparalleled multisystemic effects. The complicated clinical presentation of DM results from broad underlying molecular changes, including misprocessing of a family of genetic transcripts caused, at least in part, by sequestration of the RNA binding protein, MBNL. The complex DM phenotype follows a multiphasic time course, in which specific features appear at various ages from infancy through adulthood, each DM patient having overlapping developmental, degenerative and physiological deficits. Clinical focus on skeletal muscle in DM, although important, can obscure the devastating CNS effects of the disorder, including: developmental cognitive impairment, progressive loss of executive function, personality and behavioral changes, social interactions in the autism spectrum, and central hypersomnia. To clarify pathophysiology, and facilitate treatment of the CNS effects, the proposed studies will quantitatively characterize a clinically important but poorly defined feature, central hypersomnia, a physiological abnormality that may measurably respond to pharmacologic or genetic treatment. The sleep abnormality will be studied in the context of other defined CNS features including altered white matter integrity (using novel MRI measures), loss of executive function and measurement of CSF abnormalities. While optimism has grown for treating skeletal muscle in DM with antisense oligonucleotides, the proposed studies will now help clarify molecular pathophysiology while also defining methods for studying CNS response to treatment, and establishing methods to compare mouse models with the clinical disorder, allowing future detailed insights into the cause and treatment of this common, complex and devastating disease.